It is known that polyphenylene ether resins, including those combined with high impact polystyrene, with or without flame retardant agents are very valuable as engineering thermoplastics. Articles molded therefrom have found widespread use in consumer and military components, in the automotive, business machine, home appliance and similar areas. One drawback in some compositions is that they exhibit somewhat less than optimum adhesion and are therefore not easy to paint As a result, articles molded from polyphenylene ether resin compositions have not been entirely satisfactory where color, pattern, appearance and environmental resistance are important. Further, less than adequate adhesion to paints has made it difficult to employ these compositions in applications where coatings are applied to produce EMI shielding, anti-static properties and electrical conductivity, although it has been proposed, for example, in Haaf et al., U.S. Pat. No. 4,433,088, to use small amounts of polyolefin glycols and low molecular weight polyamides to improve paint adhesion. The latter compositions do have drawbacks, however, because such additives can lower physical properties and the compositions must be kept free of polyethylene, which is normally desirable for surface appearance and mold release purposes.
It is also known, for example, from Trementozzi, U.S. Pat. No. 4,360,618 to blend polyphenylene ether resins with styrene-acrylonitrile (SAN) or acrylonitrile-butadiene-styrene (ABS) polymers containing from 2 to 8% by weight of acrylonitrile and to obtain highly advantageous compositions in terms of molded article strength and distortion temperature. In Deets et al., U.S. Pat. No. 4,578,423, such compositions are described in which the polymers contain 8 to 17% by weight of acrylonitrile. However, there is no hint or suggestion in either patent that such polymer compositions would have improved or even adequate adhesion to paints.
It is therefore an object of the present invention to provide a method of improving the adhesion to paint of a thermoplastic composition containing a polyphenylene ether (PPO) resin and high impact polystyrene (HIPS) resin and, optionally, a flame retardant agent while retaining the properties typically associated with PPO-HIPS compositions such as high tensile strength and flexural strength.
It is a further object of the invention to provide a method of improving the adhesion of a thermoplastic composition so that the composition in the form of a molded article will retain a coating of paint even under adverse conditions, especially after soaking in water.
It is a still further object of the invention to provide a method of unexpectedly improving the flow properties of such thermoplastic compositions.